text: In organic synthesis, industrial and otherwise, the nitro group is a versatile functional group. A mixture of nitric and sulfuric acids introduces a nitro substituent onto various aromatic compounds by electrophilic aromatic substitution. Many explosives, such as TNT, are prepared this way:
  Either concentrated sulfuric acid or oleum absorbs the excess water.
  The nitro group can be reduced to give an amine group, allowing synthesis of aniline compounds from various nitrobenzenes: